1. Field of the Invention
The present invention relates to a misfire prevention system during an evaporated gas monitoring and a control method thereof, and more particularly to a misfire prevention system during an evaporated gas monitoring process and a control method thereof. An evaporated gas leakage is monitored and at the same time, the leakage is compensated in consideration of a total fuel quantity increase according to generation of the evaporated gas, thereby preventing misfire caused by a change of an air-fuel ratio.
2. Description of the Prior Art
An environmental law has been recently enacted to enforce the regulation of evaporated gas directly emitted into the atmosphere from fuel supply systems of vehicles.
In other words, where a problem involving a purge control system exists, an accurate monitoring function is necessary for the system because of significant leakage of evaporated gas.
The environmental law concerning evaporated gas control calls for a detection of leakage (diameter of 1 mm) at a purge control system to activate a warning light in case of the leakage.
The accurate monitoring on the relevant system is generally performed by checking pressure at a time when a fuel supply system is near empty.
Furthermore, monitoring is executed while an engine races and the vehicle is stopped in operation.
At an initial stage of the monitoring, when a purge control valve (pressure control solenoid valve) is opened and a shut-off valve mounted at a discharge outlet of a canister (which temporarily collects the evaporated gas) is closed, a fuel tank is evacuated at an interior thereof by negative pressure of the engine.
At this time, when the evacuated state is not detected by a pressure sensor for detecting pressure in the fuel tank, it is determined that a big leakage of evaporated gas has occurred in the purge control system.
Likewise, a small leakage of the evaporated gas can be detected by a vacuum pressure decrease rate measured at a time when the tank is airtightly shut, where the purge control valve is shut at a predetermined pressure.
The leakage is currently checked by measurement of pressure inclination changes generated by causing a fuel supply system to be evacuated.
However, there is a problem in the monitoring process of the evaporated gas leakage thus described, in that the air-fuel ratio can be changed abruptly so that a misfire could occasionally occur because the purged gas, that is the evaporated gas infused into a surge tank during the operation of the purge control valve, is not considered in the calculation of the basic fuel amount.
In order to overcome the aforementioned problem, the shut-off valve is closed at an initial stage while the engine races and the purge control valve is opened at a predetermined inclination to thereby cause the fuel supply system to be evacuated.
At this time, if an evaporated fuel concentration collected in a canister is large, the gas is infused into the surge tank by the operation of the purge control valve to thereby form a rich mixture, resulting in a severe change of the air-fuel ratio. This also causes a misfire and a decrease in stable racing.
FIG. 1 is a waveform diagram for illustrating a change in an air-fuel ratio during operation of a purge control valve according to the prior art.
As illustrated in FIG. 1, an overall fuel quantity consumed in the engine is increased by the purge gas infused into the surge tank during an operation range of a purge control valve according to the prior art, thereby varying the air-fuel ratio.